1. Field of the Invention
The present invention relates to an information terminal apparatus for receiving a satellite signal transmitted from an artificial satellite constituting a global navigation system, and further relates to an information processing apparatus and an information communication system that inquire such an information terminal apparatus for position and time information with respect to current position and/or current time.
2. Description of the Related Art
In recent times, a GNSS (Global navigation system) has become common for determining a position of moving object on the ground, utilizing artificial satellites orbiting around the earth. Typical global navigation systems are GPS (Global Positioning System) constructed by the United States of America, GLONASS Global navigation system constructed by the former Soviet Union, and GALILEO, which is being constructed mainly by European countries.
In the global navigation systems, when determining current position, signals are received from at least four satellites by means of a receiver installed on the moving object. On acquiring orbit information of each satellite by demodulating a signal from each satellite, a three-dimensional position and an accurate current time of the moving object are calculated, by means of simultaneous equations, based on the orbit information and time information of each satellite and a delay time of the received signal. The global navigation systems are widely used such that the receiver having a function of determining the current position and the current time as mentioned above (hereafter referred to as GPS function) is installed in a variety of vehicles and airplanes so as to guide routes and detect the current position of vehicles and airplanes. Also, portable positioning apparatus or devices having the GPS function installed therein have been conventionally used.
On the other hand, in recent years, the size and power consumption of a receiver, for example, has been reduced and therefore the GPS function is now being installed in a variety of information terminal apparatuses. Particularly, among portable phones (or a so-called cellular phones), which have become fast sophisticated and multifunctional, those having the GPS function have become remarkably popular.
It is typical that in addition to a basic call function and the GPS function such a portable phone has a network function allowing a variety of information communications with another information processing apparatus through a communication network such as the Internet. The information with respect to the current position acquired by means of the GPS function is communicated between the portable phone and another information processing apparatus by means of a network function so as to receive benefits from services related to the current position.
An example of such services to mantion may be a map display service where information related to the current position acquired by means of the portable phone having the GPS function is transmitted to a server apparatus via the communication network and a map data near and related to the current position is acquired from the server apparatus so as to display the data on a display screen. In a similar way, information may be communicated between the portable phone and the server apparatus so as to enjoy such services. Other examples are a navigation service for displaying a route from the current position to destination, a mail transmission service for sending, by email, information related to the current position to another portable phone or a computer apparatus, a peripheral information display service for displaying information related to different stores located in the peripheral areas about the current position, etc.
Further, considering that the communication network has become wider in bandwidth and reduced in cost, not only to the portable phone as mentioned above but also to a variety of information terminal apparatuses as represented by PDAs (Personal Digital Assistants) and small and light personal computer apparatuses, it is expected that a variety of services related to the current position will be more widely provided in conjunction with the GPS function and the network function.
In addition to the services, it has been considered that a network service system where moving people are to carry portable phones through which position/time information of the people is collected to manage the current positions of the moving people so as to be provided with their positions and indications corresponding to the current position and time.